yes some games use more than 2 gigs of ram+os uses a few, 4 isnt enought.
4 gig of RAM is more than enough for almost every gamer build .
A game is a 32 bit program and cant ever use more than about 3.3 gig of RAM , at most, for the same reason a 32 bit operating system cant .
Windows installs typically use 7-800 MB meaning that there is enough left over for the game .
You can check this yourself. Run your game in a window . Have Task manager open in another window and you can see immediately how much RAM is actually being used .